1. Field of the Invention
The present invention relates to a color picture tube device that deflects a plurality of electron beams which are emitted from an electron gun having a plurality of in-line cathodes, and displays a color image on a phosphor screen.
2. Related Art
In a color picture tube device having an in-line electron gun in which cathodes corresponding to the three colors of red (R), green (G), and blue (B) are horizontally aligned, three electron beams emitted from the electron gun need to meet in an appropriate point on a phosphor screen (this is called “convergence”). Self convergence and dynamic convergence are conventional techniques which are widely used for producing such convergence.
The self convergence technique produces convergence by generating non-uniform deflection magnetic fields for deflecting the electron beams. Typically, a horizontal deflection magnetic field and a vertical deflection magnetic field are distorted in the shapes of a pincushion and a barrel respectively. In this way, each of the three electron beams is deflected by a different amount while passing through the deflection magnetic fields, so that the three electron beams converge throughout the phosphor screen.
The dynamic convergence technique produces convergence by generating a magnetic field (a dynamic convergence magnetic field) for dynamically changing the angles of the two outer electron beams before the three electron beams are deflected. The intensity of this magnetic field is varied according to the amount of deflection, so that the three electron beams converge throughout the phosphor screen.
A self-convergent color picture tube device has a drawback that the spot shape of the three electron beams is deformed near the edges of the phosphor screen. Such a deformed spot shape causes a drop in resolution. Various techniques have been proposed to correct this (e.g. Published Unexamined Patent Application No. H09-102288). Nevertheless, these efforts cannot satisfactorily cope with the recent trends toward increasing display data density and widening deflection angle for shallow TV sets.
A dynamic-convergent color picture tube device uses uniform magnetic fields having no distortions as deflection magnetic fields, and so does not suffer from a drop in resolution. However, this type requires a complex construction.